This invention relates to exterior lead forming devices for forming exterior leads of semiconductor devices into predetermined forms.
FIG. 2 is an end view of a conventional semiconductor lead forming device. A semiconductor device 1 is positioned on a bending die 3 fixedly supported on a die plate 2. The bending die 3 positions the semiconductor device 1 precisely at a predetermined position. On the lower surface of a punch plate 4 fixed to a press ram (not shown) is attached a U-shaped forming member 5. Bending rollers 7 are rotatably supported on guide pins 6 at the ends of forming member 5. A pressing plate 8 opposing the bending die 3 is slidably attached to the punch plate 4 via a guide shaft 9, to fixedly hold the exterior leads 1a of the semiconductor device 1 on the bending die 3 during the bending of the exterior leads 1a. The guide shaft 9 urges the pressing plate 8 downward to clamp the exterior leads 1a.
The semiconductor device 1 having the exterior leads 1a which are bent and formed by the exterior leads forming device is obtained as follows. First, as shown in FIG. 3, semiconductor elements are mounted on a lead frame 10 and encapsulated with synthetic resin 11. Next, the connector portions 12 connecting the leads together and the end portions 13 of the leads are cut away to produce separate semiconductor devices, as shown in FIG. 4.
The exterior leads 1a of the semiconductor device 1 as shown in FIG. 4 are bent by means of the exterior lead forming device of FIG. 2 as follows. First, the semiconductor device 1 as shown in FIG. 4 is positioned on the bending die 3 as shown in FIG. 2. Next, the punch plate 4 is lowered such that the end surfaces 8a of the pressing plate 8 come into contact with the upper surfaces of the exterior leads 1a. The semiconductor device 1 is thus fixedly held on the bending die 3 by means of the pressing plate 8. The punch plate 4 is lowered further to bend the exterior leads 1a with the bending rollers 7 along the side surfaces of the bending die 3. The exterior leads 1a are bent in accordance with the form of the bending die 3. The bending rollers 7 rotate on respective guide pins 6 to bend the exterior leads 1a. FIGS. 5(a) and 5(b) respectively show an end view and a side view of a semiconductor device the exterior leads of which have been bent into a predetermined form.
The conventional exterior lead forming device has the following disadvantage. The totality of bending stress developed during bending of the exterior leads 1a is supported by the guide pins 6. Further, the outer circumferential surface of the guide pins 6 and the inner circumferential surface of the bending rollers 7 slide on each other in response to the forming stress. Thus, due to abrasions, a gap greater than a predetermined magnitude may be formed at the support and the rotating contact portions of the guide pins 6. If this happens, the predetermined bending form and dimension of the exterior leads 1a can no longer be obtained. Due to the resulting dimensional errors, the yield of the semiconductor device production is reduced, and reworking of the semiconductor devices may become necessary.